ELECTRON MICROSCOPE

Tariq MunirM.Phil Microbiology

DEFINITIONThe word microscope is derived from the Greek wordso mikros (small) o skopeo (look at). The electron microscope is a type of microscope that uses a beam of electrons to create an image of the specimen.

BACKGROUND OF E.M Light Microscope developed from the Galilean telescope in 17th century.

Earliest microscope invented by Antony van Leeuwenhoek (1632-1723)

in the 1920s, it was discovered that accelerated electrons behave in a vacuum much like light.

 Ernst Ruska & Max Knoll built the first transmission electron microscope (TEM) in 1931

Ruska was awarded the Nobel Prize for Physics in 1986.

WORKING OF E.MThe basic steps involved in all EMs: A stream of high voltage electrons (usually 5-100 KeV) is formed by the Electron Source (usually a heated tungsten filament) and accelerated in a vacuum toward the specimen using a positive electrical potential. 

Stream is confined and focused using metal apertures & magnetic lenses into a thin, focused, monochromatic beam.

Interactions occur inside the irradiated sample, affecting the electron beam.

These interactions and effects are detected and transformed into an image.

SCHEMATIC DIAGRAM OF WORKING

TYPES OF ELECTRON MICROSCOPES

1.Transmission Electron Microscope (TEM) :

The electron beam that has been partially transmitted through the very thin (and so semitransparent for electrons) specimen carries information about the structure of the specimen.

TYPES OF ELECTRON MICROSCOPES

2. Scanning Electron Microscope (SEM):

The Scanning Electron Microscope (SEM) produces images by detecting secondary electrons which are emitted from the surface due to excitation by the primary electron beam.

ADVANTAGES• Powerful magnification.• In scientific fields including biology and life sciences, gemology, medical and forensic sciences, metallurgy and nanotechnologies.• Technological and industrial applications, such as semiconductor inspection, computer chip manufacturing, quality control• Electron tomography,• Tissue Localization• Toxicology• Virology and structural biology

DISADVANTAGES• The main disadvantages are cost, size, maintenance,

researcher training and image artifacts resulting from specimen preparation.• This type of microscope is a large, cumbersome, expensive

piece of equipment, extremely sensitive to vibration and external magnetic fields.• Upkeep involves maintaining stable voltage supplies,

currents to electromagnetic coils/lens and circulation of cool water so the samples are not damaged or destroyed from heat given off during the process of energizing the electrons.

.• Special training is required to learn the involved processes of specimen preparation, to minimize and recognize preparation-related artifacts and to operate the microscope itself. • It needs to be kept in an area large enough to contain

the microscope as well as protect and avoid any unintended influence on the electrons• Note:-

Despite these disadvantages, EMs are assets to high-end research laboratories; this powerful piece of equipment has resulted in innumerable advances in science and industry.

Thank you for your attention